At the time of writing this, the top story on N4G is that the Killzone Shadow Force Demo is only using 1.5GB or VRAM.

To those that are tech savvy: This means that it is using 1.5GBs of geometry, textures, shaders, and buffers; basically graphics data.

While this is a huge step up from the ps3, this is not as big as news as what commentators are making it. They are saying that if they use more memory it will make the game look even better. This is not true. There is a cap to how hard the GPU can push, we do not know this details as of yet. The more memory does mean we can have higher resolution textures and more...well shit in the scene at the same time but like what I said before, there is a cap to this, which we do not know yet. This does not correlate to better graphics for more memory. Let it show that PC GPUs have on average 2GBs of dedicated VRAM, yes I know they can share some main memory but this is slow and takes time to transfer from the board to the GPU...creating a bottleneck.